1. Field of the Invention
This invention relates to removal of calculi from the body. More particularly, this invention relates to intracorporeal comminution of urinary calculi.
2. Description of the Related Art
Nowadays, lithotripsy for urinary stones can be carried out by extracorporeal shockwave lithotripsy or endoscopically. The latter approach is known as intracorporeal lithotripsy. Intracorporeal lithotripsy may be conducted by flexible or rigid ureteroscopy or percutaneous nephrolithotomy. Intracorporeal lithotripsy is typically accomplished using laser energy. However, other technologies such as ballistic lithotripsy, ultrasonic lithotripsy and electrohydraulic lithotripsy are applied by instrumentation of the urinary tract.
Current instruments for intracorporeal lithotripsy have several disadvantages:
There is poor control of the outcome. By trial and error, the urologist must manually adjust the power settings, activate the instrument, and determine that the desired outcome for the case at hand has resulted. This process is usually iterated, thereby prolonging the procedure. In addition, the parameters available for change by the urologist are limited. Moreover, there is frequently no clear relation between the instrument settings and the effect on the calculus being treated.
Stone migration away from the endoscope, known as retropulsion, is a generally undesirable effect of lithotripsy. Retropulsion creates a need to further adjust or reposition the instrument, which prolongs the procedure and increases its cost. Moreover, in the case of ureteroscopy, migration of the stone up the ureter might result in its entering the renal pelvis, which could necessitate the use of another piece of equipment to complete the procedure, thereby increasing costs and possibly increasing morbidity.
Fragmentation of the stone is a desirable effect of lithotripsy. However, conventional techniques and instruments provide limited and inefficient control over the size of the stone fragments. Typically, fragments of various sizes break off from the main body of the stone. As a rule of thumb, stone fragments, which are bigger than 2 mm must be treated either by extraction or by further fragmentation. Smaller fragments are desirable, as they may be left in place. Currently, in the case of endoscopy, the urologist can only estimate the stone size by comparing the stone with the laser fiber, which has a known diameter in the image. Such estimates may be inaccurate.
There is a tradeoff between increasing power settings, which results in more fragmentation but with a greater degree of stone migration. Furthermore, increasing the power tends to produce larger fragments. Therefore, the urologist must make a compromise.